Natural Calcium-Based Thermochemical Materials Encapsulated Latent Aluminum for Superior Heat Storage

Calcium-based thermochemical materials (TCMs) and high-temperature metal phase change materials (PCMs) have garnered significant attention as advanced thermal energy storage (TES) media. However, the widespread application of these materials is limited by critical issues, such as the easy leakage and corrosion nature of metal PCMs and the propensity of calcium-based TCMs for sintering and deactivation. This study reports a new hybrid macrocapsule using aluminum as the core PCM and dolomite as the shell precursor of TCMs, which not only perfectly encapsulate aluminum but also solve the problem of insufficient reaction activity inside calcium-based TCMs. The modified dolomite macrocapsules demonstrated enhanced cycling stability and reaction activity. At a moderate carbonation temperature of 650 °C, the effective conversion rate of the dolomite macrocapsules after 20 cycles reaches 33.43%, representing 1.48 times that of dolomite balls and 2.4 times that of CaO macrocapsules. The energy storage density achieves 833.95 kJ/kg, which is 1.25 and 1.70 times higher than dolomite balls and CaO macrocapsules, respectively. Postcycling analysis reveals the peak decomposition and carbonation rates of 0.021%/min and 0.170%/min, corresponding to 1.82 times and 1.89 times improvements over dolomite balls, and 1.6 and 3.4 times enhancements compared to CaO macrocapsules. Kinetic studies of the carbonation mechanism show that the modified macrocapsules exhibit an activation energy of 52.21 kJ/mol, which is lower than the 146 kJ/mol observed for CaO macrocapsules. These findings indicate that the as-proposed macrocapsules exhibit good cyclic stability, high reactivity, and enhanced energy storage density, demonstrating potential application in high-temperature TES systems and CO2 capture.